Large quantities of liquid egg products are pasteurized each year to produce products sold in refrigerated form with limited shelf life. See generally, Egg Pasteurization Manual (USDA Agricultural Research Service 1969). More recently, the provision of techniques for ultrapasteurizing liquid egg products has led to the marketing of liquid egg products which have extended shelf lives under refrigerated conditions.
Methods of ultrapasteurizing liquid whole egg products using indirect heat, such as contacting the liquid whole egg product to a heated surface, or direct heat, such as contact to or the injection of steam, are known. See U.S. Pat. Nos. 4,808,425 to Swartzel et al.; 5,105,724 to Swartzel and Ball; and 4,957,760 to Swartzel et al.
U.S. Pat. No. 4,091,119 to Bach discloses a method and apparatus for uniform heating of a foodstuff for preservation using high-frequency electromagnetic fields. The foodstuff (in particular, a jam, marmalade or jelly) is located in a container open at its top, and two fields, one high frequency and another ultra-high frequency, are directed as different portions of the foodstuff container. Use of a high frequency field of between 1-300 MHz, used in conjunction with an ultra-high frequency field of between 300 MHz and 5 GHz, is disclosed.
U.S. Pat. No. 4,853,238 to Huang discloses a method for treating liquid egg white or liquid whole egg in order to extend the shelf-life of the liquid egg material. The liquid egg material is subjected to microwave energy while it flows in a conduit for a time sufficient to inactivate or destroy a sufficient amount of microorganisms in the material without significantly reducing the egg protein functionality of the material.
U.S. Pat. No. 4,975,246 to Charm discloses a method and apparatus for pasteurizing and/or sterilizing heat-sensitive material using high-temperature, short-time heating to substantially destroy selected microorganisms without substantially affecting other desirable properties of the material. Heat-sensitive material, such as liquid egg product, is continually passed through a flow path, such as plastic tubing, subjected to microwave radiation to heat the material to a high temperature for a short period, and then rapidly cooled.